In recent years, electrification of automobiles and the like has been promoted for the purpose of power saving and reduction in fuel consumption. For example, a system for operating an automatic transmission, a brake, a steering wheel, and the like of the automobile with use of power of an electric motor such as a motor has been developed and brought to the market. As an electric actuator for use in such an application, there has been known an electric actuator employing a ball screw mechanism configured to convert a rotary motion generated through drive by a motor into a motion in a linear direction (see Patent Literature 1).
Moreover, in the actuator of this type, it is important to control a stroke amount or a position in a stroke direction of an operation part (namely, an actuator head) configured to output the linear motion. Thus, as means for detecting the stroke amount or the position in the stroke direction, for example, there has been given a method of coupling a link mechanism that includes a plurality of link members to a movable part (namely, a stroke shaft) performing the linear motion, and detecting an angle of the link members to detect a position of the movable part (see Patent Literature 2).